The aim of this proposal is to investigate the biological and chemical profile of murine major histocompatibility (MHC) antigens (H-2 and Ia) on neoplastic cells. Since it has been demonstrated that there are alterations of H-2 and Ia antigens on tumor cells, a concerted effort will be made to characterize the expression of these MHC antigens. In addition the biochemical makeup of both MHC antigens and tumor associated antigens (TAA), as well as their relationship to one another, on tumor cells will be determined and compared with that of MHC antigens on normal cells. Attempts will be made to assess the capacity of these antigens to elicit cellular and humoral immune responses in order to evaluate the effect of malignant transformation on these cell surface markers. Xenoantibodies to tumor associated antigens will be used to develop sensitive radioimmunoassays for TAA and to compare the cross-reactivity of TAA from various tumors. Circulating TAA will also be biochemically and immunologically characterized in order to evaluate their role in the pathology of malignant disease. In addition the appearance and quantity relationship to circulating MHC antigens will be determined and correlated with stages and locations of tumor growth. A study of quantitative changes in the expression of MHC antigens on tumor cells, as well as their relationship with neoantigens of the tumor, will provide information essential to an assessment of the role of these antigens in cell communication and control phenomena. In addition a precise determination of the time course of appearance of altered and neo-antigens both on the cell surface and in the serum will allow for a critical evaluation of the potential of these changes for immunodiagnosis and immunotherapy.